## CHAPTER 1

the doppler effect caused by a moving target allows a radar to separate .... needed for pulse compression and for coherent systems such as moving-target.

CHAPTER 1 AN INTRODUCTION TO RADAR Merrill I. Skolnik

1.1

POWER AMPLIFIER

WAVEFORM GENERATOR

LOW-NOISE AMPLIFIER LOCAL OSCILLATOR

MIXER

IF MATCHED AMPLIFIER FILTER

SECOND DETECTOR

VIDEO AMPLIFIER

DISPLAY

FIG. 1.1 Simple block diagram of a radar employing a power amplifier transmitter and a superheterodyne receiver.

The operation of the radar is described in more detail, starting with the transmitter.

7.2

Perhaps the single most useful description of the factors influencing radar performance is the radar equation which gives the range of a radar in terms of the radar characteristics. One form of this equation gives the received signal power Pr as

^ = £§X4^X^

(M)

The right-hand side has been written as the product of three factors to represent the physical processes taking place. The first factor is the power density at a distance R meters from a radar that radiates a power of Pt watts from an antenna of gain Gt. The numerator of the second factor is the target cross section a in square meters. The denominator accounts for the divergence on the return path of the electromagnetic radiation with range and is the same as the denominator of the first factor, which accounts for the divergence on the outward path. The product of the first two terms represents the power per square meter returned to the radar. The antenna of effective aperture area Ae intercepts a portion of this power in an amount given by the product of the three factors. If the maximum radar range /?max is defined as that which results in the received power Pr being equal to the receiver minimum detectable signal Smin, the radar equation may be written . PtGt A6(T R4m*x = ' 2 (4TT)Xn

(1-2)

When the same antenna is used for both transmitting and receiving, the transmitting gain Gt and the effective receiving aperture Ae are related by Gt = 4TrAJX2, where X is the wavelength of the radar electromagnetic energy. Substituting into Eq. (1.2) gives two other forms of the radar equation:

^* - jSrr

vfTr; ^ mm

a.3«)

Mna* = £&T 41TA. ^ min